(A) Sitting # Venous air embolism (VAE), the entry of gas into the peripheral or central vasculature, can occur secondary to iatrogenic complications, trauma, and even certain recreational activities.> VAE results when a large bolus of air entering the venous system can cause an air lock in the right atrium and ventricle, leading to outflow obstruction, decreased pulmonary venous return, and subsequent decreased left ventricular preload and cardiac output.> Pathogenesis of pulmonary endothelial injury may have components of platelet-fibrin thrombi from the right ventricle, cytokine release, neutrophil, platelet, and complement activation at the microvascular air-blood interface, and injury mediated by lipid peroxidation and oxygen radicals.> Physical examination may reveal the following signs: Tachycardia Tachypnea Cyanosis Altered level of consciousness Hypotension Cardiac "mill wheel" murmur-A loud, churning, machinery like murmur heard over the precordium (a late sign) Sudden loss of consciousness followed by convulsion in an intubated patient on positive-pressure ventilation Circulatory shock or sudden death (patients with severe VAE)> CAUSES:1. Primary cause of VAE is surgical procedures, especially neurosurgical procedures performed in the upright, sitting position. Anytime the operative site is more than 5 cm above the right atrium, VAE is a risk. Other surgical procedures that can lead to the infusion of air include obstetric/gynecologic procedures (cesarean section), craniofacial surgery, dental implant surgery, vascular procedures, liver transplantation, and orthopedic procedures (e.g., hip replacement, arthroscopy). The frequency of reported VAE in surgical procedures ranges from 10% in cervical laminectomy up to 80% in posterior fossa surgery.2. Second cause of VAE is iatrogenic creation of a pressure gradient for air entry. Examples include spinal needles in lumbar punctures (case report), peripheral intravenous lines, central venous catheters, pulmonary artery catheters, hemodialysis catheters, and long-term (Hickman) catheters. Most cases occur during catheter manipulation, disconnection, or removal. A pressure difference of 5 cm of H2O across a 14-gauge needle allows 100 ml of air per second to enter the venous system. The frequency of reported VAE with central catheter use ranges from 1 in 47 to 1 in 3000.3. A third cause of VAE is mechanical insufflation or infusion. Insufflation has been documented to occur during arthroscopic procedures, CO2 hysteroscopy, laparoscopy, urethral insufflation, and orogenital sexual activity during pregnancy. Infusion air entry can occur during the injection of contrast agents for CT scans, angiography, and cardiac catheterization, and during cardiac ablation procedures.4. A fourth cause of VAE is positive-pressure ventilation, which can occur during mechanical ventilation and SCUBA diving.5. Finally, blunt and penetrating trauma to the chest, abdomen, neck, and face can lead to the entry of air and ultimately to VAE